Methods for etching structures and smoothing sidewalls

ABSTRACT

A method for patterning a material layer on a substrate includes forming a hard mask layer on a material layer disposed on a substrate, the material layer comprising a plurality of first layers and a plurality of second layers alternately formed over the substrate, performing a first etch process to form features in the material layer through the hard mask layer by supplying a first etching gas, and performing a second etch process to smooth sidewalls of the features formed in the material layer by suppling a second etching gas. The first etching gas is supplied continuously and the second etching gas is pulsed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationSer. No. 63/067,117, filed on Aug. 18, 2020, which is incorporated byreference herein.

BACKGROUND Field

Embodiments of the present disclosure generally relate to etchingprocesses of structures in semiconductor applications. Particularly,embodiments of the present disclosure provide methods for etchingstacked material layers to form features therein having smoothsidewalls.

Description of the Related Art

In smaller and lighter electronic devices with higher performance andincreased features, three dimensional (3D) integrated circuits (ICs)designed with through-vias and trenches have been adapted. Through-viasand trenches are used for electrical connections which pass throughstacked material layers formed on a semiconductor wafer. The adoption ofthrough-vias and trenches has faced high costs and challenges associatedwith high volume manufacturing. One such challenge includes creatingthrough-vias and trenches with smooth sidewalls. Through-vias andtrenches with smooth sidewalls are generally more robust and can beeffectively filled with materials such as dielectrics and metals. Incontrast, through-vias and trenches with rough sidewalls (e.g.,scalloped sidewalls) can result in ineffective filling, leading toreduced yield and long-term device reliability problems. Unfortunately,existing etching methods create through-vias and trenches with roughsidewalls, and/or are impractical for high volume manufacturing. Anotherfactor influencing adoption of through-vias and trenches includes thecost of performing plasma etching, which is influenced by, for example,the overall etch rate.

Therefore, there is a need for a method for performing an etchingprocess for forming features having smooth sidewalls in material layerswith a fast etch rate.

SUMMARY

Embodiments of the present disclosure provide a method for patterning amaterial layer on a substrate. The method includes forming a hard masklayer on a material layer disposed on a substrate, the material layercomprising a plurality of first layers and a plurality of second layersalternately formed over the substrate, performing a first etch processto form features in the material layer through the hard mask layer bysupplying a first etching gas, and performing a second etch process tosmooth sidewalls of the features formed in the material layer bysuppling a second etching gas. The first etching gas is suppliedcontinuously and the second etching gas is pulsed.

Embodiments of the present disclosure also provide a method for etchinga material layer on a substrate through a hard mask in a processingchamber. The method includes supplying a first etching gas to a materiallayer having a hard mask formed thereon in a processing chamber, thematerial layer comprising a plurality of first layers and a plurality ofsecond layers alternately formed over a substrate, and subsequent tosupplying the first etching gas, supplying a second etching gas intofeatures etched in the material layer by the first etching gas. Thefirst etching gas is supplied continuously and the second etching gas ispulsed.

Embodiments of the present disclosure also provide a method forsmoothing sidewalls of features etched in a material layer. The methodincludes pulsing fluorine containing etching gas to a material layer ina processing chamber, the material layer comprising a plurality of firstlayers and a plurality of second layers alternately formed over asubstrate, and continuously supplying passivation gas and inert gas inthe processing chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentdisclosure are attained and can be understood in detail, a moreparticular description of the disclosure, briefly summarized above, maybe had by reference to the embodiments thereof which are illustrated inthe appended drawings.

FIG. 1 is a schematic cross-sectional view of a processing chamberconfigured to perform a patterning process according to one or moreembodiments of the disclosure.

FIG. 2 is a flowchart of a method for patterning a material layer on asubstrate, according to one or more embodiments of the presentdisclosure.

FIGS. 3A-3D illustrate cross sectional views of a structure during thepatterning process of FIG. 2.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements and features of oneembodiment may be beneficially incorporated in other embodiments withoutfurther recitation.

It is to be noted, however, that the appended drawings illustrate onlyexemplary embodiments of this disclosure and are therefore not to beconsidered limiting of its scope, for the disclosure may admit to otherequally effective embodiments.

DETAILED DESCRIPTION

Methods for patterning features with desired small dimensions in astacked metal layer are provided. The methods utilize a two-step etchingprocess, which includes a main etch process to form features through thestacked metal layer at a fast etch rate and a post etch process tosmooth sidewalls of the features. By doing so, features having smoothsidewalls can be formed at a high overall etch rate.

FIG. 1 is a schematic cross-sectional view of an exemplary plasmaprocessing chamber 100 suitable for performing a patterning process. Oneexample of the plasma processing chamber 100 that may be adapted tobenefit from the disclosure is an CENTRIS® Sym3™ etching processingchamber, available from Applied Materials, Inc., located in Santa Clara,Calif. It is contemplated that other process chambers, including thosefrom other manufactures, may be adapted to practice embodiments of thedisclosure.

The plasma processing chamber 100 includes a chamber body 102 having achamber volume 104 defined therein. The chamber body 102 has sidewalls106 and a bottom 108 which are coupled to ground 110. The sidewalls 106have a liner 112 to protect the sidewalls 106 and extend the timebetween maintenance cycles of the plasma processing chamber 100. Thedimensions of the chamber body 102 and related components of the plasmaprocessing chamber 100 are not limited and generally are proportionallylarger than the size of the substrate W to be processed therein.Examples of substrate sizes include 200 mm diameter, 250 mm diameter,300 mm diameter and 450 mm diameter, among others.

The chamber body 102 supports a chamber lid assembly 114 to enclose thechamber volume 104. The chamber body 102 may be fabricated from aluminumor other suitable materials. A substrate access port 116 is formedthrough the sidewall 106 of the chamber body 102, facilitating thetransfer of the substrate W into and out of the plasma processingchamber 100. The substrate access port 116 may be coupled to a transferchamber and/or other chambers of a substrate processing system (notshown).

A pumping port 118 is formed through the sidewall 106 of the chamberbody 102 and connected to the chamber volume 104. A pumping device (notshown) is coupled through the pumping port 118 to the chamber volume 104to evacuate and control the pressure therein. The pumping device mayinclude one or more pumps and throttle valves.

A gas panel 120 is coupled by a gas line 122 to the chamber body 102 tosupply process gases into the chamber volume 104. The gas panel 120 mayinclude one or more process gas sources 124, 126, 128, 130 and mayadditionally include inert gases, non-reactive gases, and reactivegases, if desired. Examples of process gases that may be provided by thegas panel 120 include, but are not limited to, hydrocarbon containinggas including methane (CH₄), sulfur hexafluoride (SF₆), silicon chloride(SiCl₄), carbon tetrafluoride (CF₄), hydrogen bromide (HBr), hydrocarboncontaining gas, argon gas (Ar), chlorine (Cl₂), nitrogen (N₂), helium(He) and oxygen gas (O₂). Additionally, process gases may includenitrogen, chlorine, fluorine, oxygen and hydrogen containing gases suchas BCl₃, C₂F₄, C₄F₈, C₄F₆, CHF₃, CH₂F₂, CH₃F, NF₃, NH₃, CO₂, SO₂, CO,N₂, NO₂, N₂O and H₂ among others.

Valves 132 control the flow of the process gases from the process gassources 124, 126, 128, 130 from the gas panel 120 and are managed by acontroller 134. The flow of the gases supplied to the chamber body 102from the gas panel 120 may include combinations of the gases.

The chamber lid assembly 114 may include a nozzle 136. The nozzle 136has one or more ports for introducing the process gases from the processgas sources 124, 126, 128, 130 of the gas panel 120 into the chambervolume 104. After the process gases are introduced into the plasmaprocessing chamber 100, the gases are energized to form plasma. Anantenna 138, such as one or more inductor coils, may be providedadjacent to the plasma processing chamber 100. An antenna power supply140 may power the antenna 138 through a match circuit 142 to inductivelycouple energy, such as RF energy, to the process gas to maintain aplasma formed from the process gas in the chamber volume 104 of theplasma processing chamber 100. Alternatively, or in addition to theantenna power supply 140, process electrodes below the substrate Wand/or above the substrate W may be used to capacitively couple RF powerto the process gases to maintain the plasma within the chamber volume104. The operation of the antenna power supply 140 may be controlled bya controller, such as controller 134, that also controls the operationof other components in the plasma processing chamber 100.

A substrate support pedestal 144 is disposed in the chamber volume 104to support the substrate W during processing. The substrate supportpedestal 144 may include an electrostatic chuck (ESC) 146 for holdingthe substrate W during processing. The ESC 146 uses the electrostaticattraction to hold the substrate W to the substrate support pedestal144. The ESC 146 is powered by an RF power supply 148 integrated with amatch circuit 150. The ESC 146 comprises an electrode 152 embeddedwithin a dielectric body. The electrode 152 is coupled to the RF powersupply 148 and provides a bias which attracts plasma ions, formed by theprocess gases in the chamber volume 104, to the ESC 146 and substrate Wpositioned thereon. The RF power supply 148 may cycle on and off, orpulse, during processing of the substrate W. The ESC 146 has an isolator154 for the purpose of making the sidewall of the ESC 146 lessattractive to the plasma to prolong the maintenance life cycle of theESC 146. Additionally, the substrate support pedestal 144 may have acathode liner 156 to protect the sidewalls of the substrate supportpedestal 144 from the plasma gases and to extend the time betweenmaintenance of the plasma processing chamber 100.

Furthermore, the electrode 152 is coupled to a power source 158. Thepower source 158 provides a chucking voltage of about 200 volts to about2000 volts to the electrode 152. The power source 158 may also include asystem controller for controlling the operation of the electrode 152 bydirecting a DC current to the electrode 152 for chucking and de-chuckingthe substrate W.

The ESC 146 may include heaters disposed therein and connected to apower source (not shown), for heating the substrate, while a coolingbase 160 supporting the ESC 146 may include conduits for circulating aheat transfer fluid to maintain a temperature of the ESC 146 andsubstrate W disposed thereon. The ESC 146 is configured to perform inthe temperature range required by the thermal budget of the device beingfabricated on the substrate W. For example, the ESC 146 may beconfigured to maintain the substrate W at a temperature of about 25degrees Celsius to about 500 degrees Celsius for certain embodiments.

The cooling base 160 is provided to assist in controlling thetemperature of the substrate W. To mitigate process drift and time, thetemperature of the substrate W may be maintained substantially constantby the cooling base 160 throughout the time the substrate W is in thecleaning chamber. In one embodiment, the temperature of the substrate Wis maintained throughout subsequent cleaning processes at about 30 to120 degrees Celsius.

A cover ring 162 is disposed on the ESC 146 and along the periphery ofthe substrate support pedestal 144. The cover ring 162 is configured toconfine etching gases to a desired portion of the exposed top surface ofthe substrate W, while shielding the top surface of the substratesupport pedestal 144 from the plasma environment inside the plasmaprocessing chamber 100. Lift pins (not shown) are selectively movedthrough the substrate support pedestal 144 to lift the substrate W abovethe substrate support pedestal 144 to facilitate access to the substrateW by a transfer robot (not shown) or other suitable transfer mechanism.

The controller 134 may be utilized to control the process sequence,regulating the gas flows from the gas panel 120 into the plasmaprocessing chamber 100 and other process parameters. Software routines,when executed by the CPU, transform the CPU into a specific purposecomputer (controller) that controls the plasma processing chamber 100such that the processes are performed in accordance with the presentdisclosure. The software routines may also be stored and/or executed bya second controller (not shown) that is collocated with the plasmaprocessing chamber 100.

FIG. 2 is a flow diagram of a method 200 for patterning a material layerdisposed on a substrate. FIGS. 3A-3D are cross-sectional views of aportion of a structure 300 formed on a substrate 302 corresponding tovarious stages of the method 200. The method 200 may be utilized to etchhigh aspect ratio features, e.g., greater than 10:1 in a material layer.Although the method 200 is described below with reference to etching aconductive material layer having a stair-like structures, the method 200may also be used for manufacturing other types of structures.

The substrate 302 may be a silicon based material or any suitableinsulating materials or conductive materials as needed. The substrate302 may include a material such as crystalline silicon (e.g., Si<100> orSi<111>), silicon oxide, strained silicon, silicon germanium, doped orundoped polysilicon, doped or undoped silicon wafers and patterned ornon-patterned wafers, silicon on insulator (SOI), carbon doped siliconoxides, silicon nitride, doped silicon, germanium, gallium arsenide,glass, or sapphire. The substrate 302 may have various dimensions, suchas 200 mm, 300 mm, 450 mm or other diameter wafers, as well as,rectangular or square panels. Unless otherwise noted, implementationsand examples described herein are conducted on substrates with a 200 mmdiameter, a 300 mm diameter, or a 450 mm diameter substrate. In theimplementation wherein a SOI structure is utilized for the substrate302, the substrate 302 may include a buried dielectric layer disposed ona silicon crystalline substrate. In the example depicted herein, thesubstrate 302 is a crystalline silicon substrate.

The structure 300 may include a multi-material layer 304 formed ofconductive material and utilized to be part of an integrated circuit,such as gate electrodes, interconnect lines, and contact plugs. In someembodiments, the multi-material layer 304 includes a number of stackedlayers formed on the substrate 302 as shown in FIG. 3A. Themulti-material layer 304 may include first layers 306 and second layers308 alternately formed over the substrate 302. Although FIG. 3A showssix repeating layers of first layers 306 and second layers 308alternately formed on the substrate 302, any desired number of repeatingpairs of first layers 306 and second layers 308 may be utilized asneeded.

In some examples, the multi-material layer 304 may be formed ofrefractory metals, such as tungsten (W), molybdenum (Mo), tantalum (Ta),titanium (Ti), hafnium (Hf), vanadium (V), chromium (Cr), manganese(Mn), ruthenium (Ru), alloys thereof, silicide compounds thereof,nitride compounds thereof, or combinations thereof. In other examples,the first layers 306 and the second layers 308 may be other metals, suchas copper (Cu), nickel (Ni), cobalt (Co), iron (Fe), aluminum (Al),palladium (Pd), gold (Au), silver (Au), platinum (Pt), alloys thereof,nitride compound thereof, or combinations thereof. In one embodiment,the first layers 306 are formed of molybdenum (Mo) and the second layers308 are formed of tungsten (W). The multi-material layer 304 may have atotal thickness of between about 200 nm and about 4500 nm. The firstlayers 306 may each have a thickness of between about 10 nm and about 30nm. The second layers 308 may each have a thickness of between about 10nm and about 30 nm.

The method 200 begins at block 202 by, prior to an etching process,forming an etch resist hard mask (referred to as a “hard mask”hereinafter) 310 on the multi-material layer 304 in a processingchamber. As shown in FIG. 3B, the structure 300 includes the hard masklayer 310 formed in a desired pattern on the multi-material layer 304.The pattern on the hard mask layer 310 may have openings 314 having adimension of between about 1000 nm and about 1300 nm, to form featureshaving a high aspect ratio (e.g., greater than about 5:1), and a pitchbetween adjacent openings 314 of between about 50 nm and about 180 nm.The structure 300 includes an adhesion layer 312 formed between themulti-material layer 304 and the hard mask layer 310. The adhesion layer312 may function as a barrier layer between the multi-material layer 304and the hard mask layer 310. The adhesion layer 312 may also function asa polish stop for a subsequent chemical mechanical polishing (CMP) step.

The hard mask layer 310 may be formed of tetra-ethyl-orthosilicate(TEOS) or silicon oxynitride (SiON) and have a thickness 316 of about500 nm and about 2 μm. The adhesion layer 312 may be formed of anydielectric material, such as silicon nitride (Si₃N₄) and have athickness of less than about 100 nm. The hard mask layer 310 and theadhesion layer 312 may be deposited by any conventional depositionprocess, such as a chemical vapor deposition (CVD) process, a physicalvapor deposition (PVD) process, an atomic layer deposition (ALD)process, and a spin-on process, and subsequently patterned by aconventional photolithographic process using a patterned photoresistlayer (not shown) covering the hard mask layer 310.

At block 204, a first etching process (also referred to as a “main etch”process) is performed to form features 318 (e.g., trenches or vias) inthe multi-material layer 304 through the hard mask layer 310 usingplasma excited species or radicals in a plasma process chamber, such asthe plasma processing chamber 100 depicted in FIG. 1. In the main etchprocess at block 204, the multi-material layer 304 is etched usingchlorine containing etching gas to a predetermined depth as chlorinecontaining etching gas provides a fast etch rate for the multi-materiallayer 304. The main etch process may be continued until a depth of thefeatures 318 in the multi-material layer 304 reaches a predetermineddepth. In some embodiments, the determined depth of the features 318 inthe multi-material layer 304 is between about 200 nm and about 4500 nm.

Suitable examples of the chlorine containing etching gas include Cl₂,SiCl₄, BCl₃, SiHCl₃, SiH₂Cl₂, SiH₃Cl, and Si₂Cl₆. In one particularexample, the chlorine containing etching gas includes SiCl₄, Cl₂, andBCl₃.

In some embodiments, the main etch process is performed bysimultaneously supplying the chlorine containing etching gas and inertgas such as argon (Ar).

During the main etch process at block 204, several process parametersmay also be regulated. In one example, Cl₂, SiCl₄, and BCl₃ gases may besupplied at flow rates of between about 100 sccm and about 1000 sccm,for example, about 490 sccm, between about 10 sccm and about 140 sccm,for example, about 30 sccm, and between about 100 sccm and about 500sccm, for example, about 300 sccm, respectively. Inert gas such as argon(Ar) may be supplied at a flow rate of less than about 900 sccm, forexample, about 400 sccm. In one exemplary embodiment, a process pressurein the plasma processing chamber 100 is regulated between about 10 mTorrand about 50 mTorr, for example, about 20 mTorr.

An RF source and/or bias power may be utilized while performing the mainetch process at block 204. The RF bias power applied when supplying theetching gas assists in forming the reactive etchants with desireddirectionality so as to travel down to surfaces of the multi-materiallayer 304 that is exposed from the hard mask layer 310 to predominatelyetch the multi-material layer 304. In contrast, the elimination of theRF bias power can assist the reactive species in the plasma to be moreuniformly distributed across the hard mask layer 310. For example, an RFsource power of between about 500 Watts and about 2000 Watts may beapplied to maintain a plasma inside the processing chamber 100. An RFbias power of between about 500 Watts and about 6000 Watts may beapplied.

A substrate support pedestal to support the substrate 302, such as thesubstrate support pedestal 144 disposed in the plasma processing chamber100, is maintained at a temperature of between about 50° C. and about290° C., for example about 110° C. during the main etch process at block204.

In the main etch process at block 204, due to a difference between anetch rate of the first layers 306 and an etch rate of the second layer308, the etched features 318 (e.g. trenches or vias) in themulti-material layer 304 may have rough sidewalls having concaves inscallop-like shapes (referred to as “scallops”) or other rough features.In the example shown in FIG. 3C, the first layers 306 formed of, forexample, molybdenum (Mo), have a faster etch rate than the second layers308 formed of, for example, tungsten (W) during the main etch process atblock 204 using chlorine containing etching gas mixture. As a result,the first layers 306 are recessed (referred to as “scalloped”) ascompared to the second layer 308.

At block 206, a second etching process (also referred to as a “postetch” process) is performed to smooth the rough sidewalls of thefeatures 318 etched in the main etch process at block 204. In theexample shown in FIGS. 3C and 3D, the sidewalls of the features 318formed in the multi-material layers 304 are etched in the post etchprocess at block 206. The second layers 308 formed of, for example,tungsten (W) have a faster etch rate than the first layers 306 formedof, for example, molybdenum (Mo) during the post etch process at block206 using fluorine containing etching gas. As a result, the protrusionsformed of tungsten (W) on the sidewalls of the features 318 are removedor reduced to scallops having a depth of less than about 1.5 nm and thenthe sidewalls of the features 318 are smoothed. Suitable examples of thefluorine containing etching gas include SF₆, CH₂F₄, C₄F₈, CF₄, CHF₃,C₂F₆, C₃F₈, or NF₃, HF.

In some embodiments, the post etch process is performed bysimultaneously supplying the fluorine containing etching gas,passivation gas, and inert gas such as argon (Ar) in the plasmaprocessing chamber.

The passivation gas selectively passivates the sidewalls of the features318 to reduce bowing profiles of the sidewalls of the features 318.Suitable examples of the passivation gas include HBr, BCl₃, SF₆, or H₂S.In one particular example, the fluorine containing etching gas includesSF₆, and the passivation gas includes HBr.

The inert gas such as argon (Ar) at a high flow rate to generate lowpressure at or near the bottom of the features 318 in the multi-materiallayer 304 such that the second etching gas reaches the bottom of thefeatures 318 in the multi-material layer 304. Thus, the sidewalls of thefeatures 318 can be smoothed.

During the post etch process at block 206, several process parametersmay also be regulated. In one example, SF₆ and HBr gases may be suppliedat flow rates of between about 25 sccm and about 150 sccm, for example,about 50 sccm, and between about 10 sccm and about 1000 sccm, forexample, about 50 sccm, respectively. Inert gas such as argon (Ar) maybe supplied at a flow rate of between 100 sccm and about 1000 sccm, forexample, about 900 sccm. The fluorine containing etching gas is suppliedpulsed at a pulse duration of between about 1 seconds and about 10seconds, for example, about 5 seconds. A duty cycle (i.e., a ratio of an“on” period in which the fluorine containing etching gas is supplied toan “off” period in which the fluorine containing etching gas is notsupplied) may be between about 1:3 and about 3:1, for example, about1:1. The post-etch process at block 206 may be repeated for betweenabout 6 seconds and about 1800 seconds, for example, about 40 seconds,corresponding to about 4 pulse cycles-depending on the total thicknessof the multi-material layer 304. In one exemplary embodiment, a processpressure in the plasma processing chamber 100 is regulated between about10 mTorr and about 5000 mTorr, such as between about 20 mTorr and about500 mTorr.

An RF source and/or bias power may be utilized while performing theetching process. For example, a RF source power of less than about 2000Watts may be applied to maintain a plasma inside the processing chamber100. An RF bias power of less than about 6000 Watts may be applied whenthe fluorine containing etching gas is supplied, and an RF bias power ofbetween about 1000 Watts and about 6000 Watts may be applied.

The plasma processing chamber is maintained at a temperature of betweenabout 75° C. and about 110° C., for example about 110° C. at the postetch process at block 206.

In some embodiments, a flow rate of the SF₆, the number of SF₆ pulseperiods, and the temperature in the plasma processing chamber areadjusted to modulate smoothness of the sidewalls (e.g., a depth ofscallops) of the features 318.

Benefits of the present disclosure include improvement in patterningfeatures with accurate and uniform profiles for three dimensional (3D)stacking of semiconductor chips. The methods according to theembodiments disclosed herein utilize a two-step etching process, whichincludes a main etch process to form features through a stacked metallayer by continuously supplying chlorine containing etching gas, and apost etch process to smooth sidewalls of the features through thestacked metal layer by pulsing fluorine containing etching gas. The mainetch process provides a fast etch rate through the stacked metal layerwhile the post etch process is adjusted to smooth the sidewalls of thefeatures at a desired smoothness. By doing so, features having smoothsidewalls can be formed at a high overall etch rate.

While the foregoing is directed to embodiments of the presentdisclosure, other and further embodiments of the disclosure may bedevised without departing from the basic scope thereof, and the scopethereof is determined by the claims that follow.

We claim:
 1. A method for patterning a material layer on a substrate,comprising: forming a hard mask layer on a material layer disposed on asubstrate, the material layer comprising a plurality of first layers anda plurality of second layers alternately formed over the substrate;performing a first etch process to form features in the material layerthrough the hard mask layer by supplying a first etching gas; andperforming a second etch process to smooth sidewalls of the featuresformed in the material layer by suppling a second etching gas, whereinthe first etching gas is supplied continuously and the second etchinggas is pulsed.
 2. The method of claim 1, wherein the plurality of firstlayers comprises molybdenum (Mo) and the plurality of second layerscomprise tungsten (W).
 3. The method of claim 1, wherein the materiallayer has a thickness of between 200 nm and 4500 nm, and the pluralityof first layers and the plurality of second layers each have a thicknessof between 10 nm and 30 nm.
 4. The method of claim 1, wherein during thesecond etch process, passivation gas and inert gas are also supplied. 5.The method of claim 4, wherein the first etching gas comprises Cl₂, andthe second etching gas comprises SF₆.
 6. The method of claim 4, whereinthe passivation gas comprises HBr, and the inert gas comprises Ar. 7.The method of claim 6, wherein during the second etch process, thesecond etching gas is pulsed at a pulse duration of between 1 secondsand 10 seconds and a duty cycle of between 1:3 and 3:1.
 8. The method ofclaim 1, wherein the hard mask layer comprises tetra-ethyl-orthosilicate(TEOS).
 9. A method for etching a material layer on a substrate througha hard mask in a processing chamber, comprising: supplying a firstetching gas to a material layer having a hard mask formed thereon in aprocessing chamber, the material layer comprising a plurality of firstlayers and a plurality of second layers alternately formed over asubstrate; and subsequent to supplying the first etching gas, supplyinga second etching gas into features etched in the material layer by thefirst etching gas, wherein the first etching gas is suppliedcontinuously and the second etching gas is pulsed.
 10. The method ofclaim 9, wherein the plurality of first layers comprises molybdenum (Mo)and the plurality of second layers comprise tungsten (W).
 11. The methodof claim 9, wherein the material layer has a thickness of between 200 nmand 4500 nm, and the plurality of first layers and the plurality ofsecond layers each have a thickness of between 10 nm and 30 nm.
 12. Themethod of claim 9, wherein while the second etching gas is supplied,passivation gas and inert gas are also supplied.
 13. The method of claim12, wherein the first etching gas comprises Cl₂, and the second etchinggas comprises SF₆.
 14. The method of claim 12, wherein the passivationgas comprises HBr, and the inert gas comprises Ar.
 15. The method ofclaim 14, wherein the second etching gas is pulsed at a pulse durationof between 1 seconds and 10 seconds and a duty cycle of between 1:3 and3:1.
 16. A method for smoothing sidewalls of features etched in amaterial layer, comprising: pulsing fluorine containing etching gas to amaterial layer in a processing chamber, the material layer comprising aplurality of first layers and a plurality of second layers alternatelyformed over a substrate; and continuously supplying passivation gas andinert gas in the processing chamber.
 17. The method of claim 16, whereinthe plurality of first layers comprises molybdenum (Mo) and theplurality of second layers comprise tungsten (W).
 18. The method ofclaim 16, wherein the fluorine containing etching gas comprises SF₆, andthe passivation gas comprises HBr.
 19. The method of claim 16, whereinthe inert gas comprises Ar.
 20. The method of claim 19, wherein thefluorine containing etching gas is pulsed at a pulse duration of between1 seconds and 10 seconds and a duty cycle of between 1:3 and 3:1.